Calculation of the vibronic structure of the photodetachment spectra of CCCl- and CCBr-

Kinetically-Controlled Growth of Chestnut-Like Au Nanocrystals with High-Density Tips and Their High SERS Performances on Organochlorine Pesticides

A modified seed growth route was developed to fabricate the Au nanocrystals with high-density tips based on kinetically-controlled growth via adjusting the adding rate of Au seeds into growth solution. The obtained Au nanostructures were chestnut-like in morphology and about 100 nm in size. They were built of the radial [111]-oriented nanoneedles and were 30⁻50 nm in length. There were about 120⁻150 tips in each nanocrystal. The formation of chestnut-like Au nanocrystals is ascribed to surfactant-induced preferential growth of seeds along direction [111]. Importantly, the chestnut-like Au configuration displayed powerful surface enhanced Raman scattering (SERS) performance (enhance factor > 10⁷), owing to the high density of tips. Further, such film was used as a SERS substrate for the detection of lindane (γ-666) molecules (the typical organochlorine pesticide). The detection limit was about 10 ppb, and the relationship between SERS intensity I and concentration C of 666 accords with the double logarithm linear. This work presents a simple approach to Au nanocrystal with high-density tips, and provides a highly efficacious SERS-substrate for quantitative and trace recognition of toxic chlorinated pesticides.

Probing the electronic structure and Au-C chemical bonding in AuC2(-) and AuC2 using high-resolution photoelectron spectroscopy

We report photoelectron spectroscopy (PES) and high-resolution PE imaging of AuC2(-) at a wide range of photon energies. The ground state of AuC2(-) is found to be linear (C∞v, (1)Σ(+)) with a …8π(4)4δ(4)17σ(2)9π(4)18σ(2) valence configuration. Detachments from all the five valence orbitals of the ground state of AuC2(-) are observed at 193 nm. High-resolution PE images are obtained in the energy range from 830 to 330 nm, revealing complicated vibronic structures from electron detachment of the 18σ, 9π, and 17σ orbitals. Detachment from the 18σ orbital results in the (2)Σ(+) ground state of neutral AuC2, which, however, is bent due to strong vibronic coupling with the nearby (2)Π state from detachment of a 9π electron. The (2)Σ(+)-(2)Π vibronic and spin-orbit coupling results in complicated vibronic structures for the (2)Σ(+) and (2)Π3/2 states with extensive bending excitations. The electron affinity of AuC2 is measured accurately to be 3.2192(7) eV with a ground state bending frequency of 195(6) cm(-1). The first excited state ((2)A') of AuC2, corresponding to the (2)Π3/2 state at the linear geometry, is only 0.0021 eV above the ground state ((2)A') and has a bending frequency of 207(6) cm(-1). The (2)Π1/2 state, 0.2291 eV above the ground state, is linear with little geometry change relative to the anion ground state. The detachment of the 17σ orbital also results in complicated vibronic structures, suggesting again a bent state due to possible vibronic coupling with the lower (2)Π state. The spectrum at 193 nm shows the presence of a minor species with less than 2% intensity relative to the ground state of AuC2(-). High-resolution data of the minor species reveal several vibrational progressions in the Au-C stretching mode, which are assigned to be from the metastable (3)Π2,1,0 spin-orbit excited states of AuC2(-) to the (2)Π3/2,1/2 spin-orbit states of neutral AuC2. The spin-orbit splittings of the (3)Π and (2)Π states are accurately measured at the linear geometry. The current study provides a wealth of electronic structure information about AuC2(-) and AuC2, which are ideal systems to investigate the strong Σ-Π and spin-orbit vibronic couplings.